
theorem Th16:
  for L being RelStr, R being auxiliary(i) (Relation of L), C
  being set, y being Element of L holds SetBelow (R,C,y) is_<=_than y
proof
  let L be RelStr, R be auxiliary(i) (Relation of L), C be set, y be Element
  of L;
  let b be Element of L;
  assume b in SetBelow (R,C,y);
  then [b,y] in R by Th15;
  hence thesis by WAYBEL_4:def 3;
end;
